Towable hydrofoil water sports devices for supporting a human rider are described in U.S. Pat. No. 5,100,354, granted Mar. 31, 1992, U.S. Pat. No. 5,249,998, granted Oct. 5, 1993, U.S. Pat. No. 6,179,676, Jan. 30, 2001, and U.S. Pat. No. 6,551,158, granted Apr. 22, 2003
These towable water sports devices have a strut, fuselage and front and rear wings or blades which are made by casting a molten aluminum alloy. This process requires pouring molten aluminum into a sand or steel mold. The alloy used in this process is, for example, a 356A aluminum which is then heat-treated to T-6 hardness. The casting is then ground or sanded down to eliminate all entry gates, all venting gates and the receiving canals. This requires a lot of grinding, sanding and machining of the cast part after it has been taken out of the mold. Another disadvantage in manufacturing using the cast process is that the metal as it cures releases or gives off gases, resulting in the production of many small voids. This porosity in the part results in a poor finish. In addition as the casting comes out of the mold, there is shrinkage and the extent of the shrinkage is variable due to the nature of the alloy and weather conditions during the curing process. The primary disadvantage of a part cast from 356A aluminum is that it does not have the ability to flex which can result in a catastrophic failure or breakage of the part. There is a large rejection rate when casting an aluminum part due to the temperature of the mold, the outside temperature, and the amount of the metal as it is poured into the mold. The temperature of the mold has to be compatible with the heat of the material poured into the mold and this changes on a daily basis. There is a lack of overall consistency in the parts. The porosity of the cast part is present on the surface of the part. The surface porosity of the cast part adds drag to the foil assembly, which hinders the performance of the hydrofoil assembly. The porosity of the cast part also is not compatible with and does not accept the anodizing process. The anodizing is, however, desirable in that it offers a protective, maintenance free and corrosion-resistant finish.
In a subsequent development, the strut, fuselage and wings or blades have been cut and ground from a single pressed or rolled aluminum or aluminum alloy billet. This process wastes a lot of metal and also requires a lot of machine time. Moreover, since all of the parts are derived from a single billet, the grain that is naturally present in the pressed or rolled aluminum all runs in the same direction throughout. As a result, the grain runs in the same direction in both the strut and the fuselage. The billet is weaker and more subject to snapping off and breaking when force is applied with the grain than when force is applied across the grain. For example, if the billet has been ground and machined so that the grain runs in the same direction as the long dimension of the strut, this means that the grain runs crosswise, across the short or lateral dimension of the fuselage in which case the strut is quite strong and break resistant when towed through the water since the force is mainly across the grain while at the same time, the fuselage is relatively weak and subject to failure since the elongate fuselage when towed at high speed is subject to powerful lateral forces when the fuselage becomes out of alignment with the direction of the tow (which is often the case). When the fuselage lands from a jump, the forces of the water pressure on the wings and wing bolt holes often result in breakage.
Another advantage to extruding the strut is that it allows for the ready shortening or lengthening of the strut to any desired length, that is, one is not married to one length as determined by mold size as in the case in casting the strut.